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Biomedical subjects

R Alvarez

Publications and source records attributed to R Alvarez.

At least 235 records · Page 13Linked to original sources
PubMed1983

[Azomonas agilis in the surface water of the environs of Buenos Aires].

In 1941, it was reported the presence of Azomonas agilis in rivers near Buenos Aires City. To our knowledge no other study has been carried out since then, so that the object of this paper was to investigate some characteristics of this organism and its possible influence on the nitrogen balance in waters. The isolation was performed by the plate method, using a mineral base for Azotobacter with different energy sources. Calcium malate appeared to be the best for Azomonas-like organisms. On pure cultures were performed tests to describe the main properties. All the organisms isolated had similar morphology, big cells 3 x 5 mu, individuals or sometimes in pairs, with intracellular granules and Gram negative. Cysts were not formed and motility was very intense in all cases. Physiologically they all were strictly aerobic, catalase positive and able to reduce acetylene so it was confirmed they belonged to the genus Azomonas. Some of them could use glucose and produced a water soluble green pigment, fluorescent under ultraviolet light which are the main characteristics of Azomonas agilis. Others lacked one of this properties but also were considered to be this species because they were very different from Azomonas insignis. One strain remained labelled only as Azomonas sp because it did not show characters of any of the two species. Estimations of bacterial density by most probable number method indicated that this was very low and by using a colorimetric determination for ethylene no nitrogenase activity could be detected in the river water, adding or not glucose even after 48 h of incubation.(ABSTRACT TRUNCATED AT 250 WORDS)

Argentina↗
PubMed1983

Selective utilization of vitamins A1 and A2 by goldfish photoreceptors.

The rhodopsin/porphyropsin (visual pigment) ratios in the goldfish retina were induced to change over a 300-day treatment period of specified light and temperature conditions. A concomitant but much slower change in the ratios of retinyl/3-dehydroretinyl ester in the pigment epithelium (RPE) was observed. If the changes in the visual pigment ratios were dependent on the nonselective sequestering of chromophores from the RPE ester pool, then the visual pigment changes might mirror those of the esters in the RPE. However, the relatively greater rate of visual pigment changes compared to that of the RPE esters suggests that goldfish photoreceptors synthesize their visual pigment from a relatively small pool of chromophore precursor rather than from the overall pool of retinyl and 3-dehydroretinyl esters stored in the RPE.

Animals↗
PubMed1982

[Circulating immune complexes in the serum of tumor patients].

The conditions for the detection of circulating immune complexes (CIC) were established by combination of polyethylene glycol precipitation with a nephelometric determination on the precipitate of endogenous C1q. The CIC precipitated from the sera of patients with breast carcinoma, malignant melanoma or autoimmune diseases were dissociated in SDS-beta-mercaptoethanol buffer and no differences were observed in the electrophoretic patterns os polyacrylamide gels allowing to characterize tumour specific antigens.

Antigen-Antibody Complex↗
PubMed1980

Phosphate exchange between high-energy phosphate compounds in resting crustacean muscle.

Single giant muscle fibres from Megabalamus psittacus was microinjected with ATP-32P or internally perfused with a solution containing 32P-PArg in an attempt to demonstrate, in the absence of inhibitiors, ATP utilization during mechanical activity with negative results. The rate constant of transfer of 32P from microinjected 32P-PArg to endogenous ATP was studied at two different temperatures, obtaining a Q10 of 1.08 +/- .012. It is concluded that the rate limiting step in the process of transference of phosphate in the resting muscle from balanus is the intracellular diffusion of PArg and not the rate at which the equivalent of Lohman's reaction in invertebrates proceeds.

Adenosine Diphosphate↗
PubMed1980

A quantitative comparative analysis of fracture healing under the influence of compression plating vs. closed weight-bearing treatment.

The study compared the healing of fractures treated with rigid immobilization with the healing of fractures without internal fixation. Comparative studies were made of the cytologic, morphologic and mechanical properties of callus from closed fractures in 2 groups of dogs: one plated, the other not. Significant differences were observed in the 2 groups in early stages of healing. The biomechanical differences between the 2 groups persisted into later stages of healing, even after histologic and electron microscopic appearance of cellular activity and new bone formation had become similar. In general, closed, nondisplaced fractures of dogs' radii treated without surgical procedures and followed by early functional activity demonstrated a cytologically more active endosteal callus and increased biomechanical strength characteristics at the fracture site.

Animals↗
PubMed1977

Activation of cardiac adenylate cyclase: horminal modification of the magnesium ion requirement.

Histamine and epinephrine stimulate the activity of guinea pig heart adenylate cyclase [ATP pyrophosphate-lyase (cyclizing) EC 4.6.1.1], in part, by decreasing the requirement for Mg2+ as an activator. This effect may represent an increase in affinity for Mg2+ and/or a decrease in sensitivity of the enzyme towards inhibition by free ATP. Both of these inotropic hormones also increase maximum velocity. Pretreatment of the membrane-bound enzyme with EDTA, to remove available divalent cations, almost eliminates persistent stimulation by guanyl-5'-yl imidodiphosphate [Gpp(NH)p]. Addition of Mg2+ to the preincubation medium restores the capacity of Gpp(NH)p to acutely activate the enzyme. These results indicate that Mg2+ interacts with the nucleotide (GTP) regulatory site. Persistent stimulation of the enzyme by either Gpp(NH)p or fluoride ion also involves a decrease in the requirement for Mg2+ and an increase in maximum velocity.

Adenosine Triphosphate↗
PubMed1977

Differences in pulmonary and cardiovascular beta receptors in the guinea pig and rabbit.

An in vivo preparation, in which a body plethysmograph was incorporated, was useful in monitoring the cardiopulmonary effects of pharmacological agents in the guinea pig and rabbit. Isoproterenol, given 30 seconds prior to histamine challenge, reproducibly blocked histamine-induced dynamic compliance decreases and increased heart in the artificially ventilated guinea pig. These effects were used to separate the activity of beta adrenergic blockers on airway and heart muscle. Dose-response data were obtained and ED50 values for pulmonary and cardiovascular blockade were compared. Relative potencies and cardioselectivity ratios for dichloroisoproterenol, practolol, dl-propranolol and d-propranolol were determined. Both practolol and dichloroisoproterenol were cardioselective; dl-propranolol was found to be the most potent. When a similar protocol was tried in the rabbit, isorpoterenol failed to antagonize either histamine or methacholine-induced airway constriction. This finding was supported in subsequent in vitro tests. Isoproterenol and epinephrine were ineffective in blocking methacholine-induced tracheal chain contractions and epinephrine did not significantly enhance adenylate cyclase activity. Our observations suggest rabbit airway smooth muscle is insensitive to beta adrenergic stimulants.

Adenylyl Cyclases↗